Getting into the details of the electrical system

The electrical systems on most modern cars consist of negative earth circuits. The main power source is the 12 volt battery and when the engine is running, the alternator. The systems run off a positive flow with a negative earth return through the body of the vehicle. On some older vehicles the system is run on a positive earth, but this is mainly on 6 volt systems.

A set of wiring looms, which is all the cables bound together which run through the vehicle and branch of where power is needed for individual components. In addition there is a heavier cable running the main charging, ignition and the starter motor to supply the high voltage required to turn and start the engine and keep the battery charged. The wiring for all the circuits in the car are of different thickness and amperage depending on the components power requirements. The wires are colour coded to enable tracing wires when looking for a fault. On modern cars with electronic control devices and components, printed circuits are widely used as they take up less space than a bunch of wires. The power source for the electrical systems is switched on via the ignition key/switch apart from the lighting system which is on a live feed to enable the lights to be used for parking. This ensures that the battery will not be run down when the car is left unattended.

The power source runs through a fuse box and relays, which protects components from damage due to electrical short outs. Apart from the starter motor most components run on 5 amp. 10 amp, 15 amp, 20 amp, 25 amp and 30 amp wiring and are fused according to the power requirements being carried on each wire. Components are activated through the ignition, relays and switches and with remote controlled devices through electromagnetic switches.

What if something goes wrong with the electrical system?

The most common faults with the electrical system involve the lighting system of the vehicle requiring the replacement of blown bulbs. In the event of a malfunction of any component, the fuses should be checked in the fuse box, normally located in the front footwells or glove compartment. This box has a labelled colour coded fuse array and individual fuses can be visually checked to see if it has blown. This serves as a starting point to resolving electrical faults.